The stellar distribution in ultra-faint dwarf galaxies suggests deviations from the collision-less cold dark matter paradigm

TL;DR

This study analyzes the stellar distributions in ultra-faint dwarf galaxies and finds evidence that challenges the collisionless cold dark matter paradigm, suggesting alternative dark matter models may better explain these galaxies.

Contribution

It provides observational evidence that the stellar distributions in UFDs are inconsistent with standard CDM potentials, supporting alternative dark matter theories.

Findings

Observed stellar profiles have cores incompatible with CDM predictions

Statistical analysis rejects CDM potential at >97% confidence

Cored potentials from alternative DM models fit the data well

Abstract

Unraveling the nature of dark matter (DM) stands as a primary objective in modern physics. Here we present evidence suggesting deviations from the collisionless Cold DM (CDM) paradigm. It arises from the radial distribution of stars in six Ultra Faint Dwarf (UFD) galaxies measured with the Hubble Space Telescope (HST). After a trivial renormalization in size and central density, the six UFDs show the same stellar distribution, which happens to have a central plateau or core. Assuming spherical symmetry and isotropic velocities, the Eddington inversion method proves the observed distribution to be inconsistent with potentials characteristic of CDM particles. Under such assumptions, the observed innermost slope of the stellar profile discards the UFDs to reside in a CDM potential at a > 97% confidence level. The extremely low stellar mass of these galaxies, 10**3-10**4 Msun , prevents stellar feedback from modifying the shape of a CDM potential. Other conceivable explanations for the observed cores, like deviations from spherical symmetry and isotropy, tidal forces, and the exact form of the used CDM potential, are disfavored by simulations and/or observations. Thus, the evidence suggests that collisions among DM particles or other alternatives to CDM are likely shaping these galaxies. Many of these alternatives produce cored gravitational potentials, shown here to be consistent with the observed stellar distribution.